1. Field of the Invention
This invention relates to an apparatus for developing a resist film, in particular to an apparatus for feeding a developer onto a resist film, and to a method for effecting the same.
2. Description of the Prior Art
In the field of fine precision processing, particularly in the process of manufacturing a semiconductor integrated circuit, it is often necessary to coat a base plate, such as a silicon wafer, with resist, such as photoresist, to form a photoresist film thereon and then subject it to exposure to provide a photoresist film having a predetermined photosensitive pattern. Next, the exposed photoresist film having a predetermined pattern is developed with a developer, such as an organic alkaline solution, and the rest of the resist film is removed to form a predetermined pattern of photoresist film on the base plate. The photoresist film thus obtained is used, for example, as a photomask to etch the base plate, as is well known.
Recently, in view of high-speed processing and economic factors, there has been a demand for a high-integration photoresist pattern. In order to satisfy this demand, it is necessary to provide a uniform and smooth photoresist film and to decrease or eliminate unevenness or irregularity in developing. There are known two methods of developing photoresist film, one being a paddle method in which a developer is dropped onto the photoresist film coated on the base plate of the semiconductor and the other being a spray method in which a developer is sprayed onto the photoresist film in the form of a mist with a spray nozzle.
However, the paddle method has a disadvantage in that it requires a large amount of developer and a considerable amount of time for developing, particularly in the case of positive developing. Also, the paddle method has a grave disadvantage in that the developing tends to be nonuniform. The reason for this is that the developing is begun near the center of the resist film (i.e., the base plate) and progresses toward the periphery of the resist film, in view of a difference in surface area between the center portion and the peripheral portion of the resist film. Namely, since the surface area of the peripheral portion is somewhat larger than that of the center portion, the center portion is overdeveloped when the developing of the peripheral portion is completed. Overdeveloping of the center portion renders the thickness of and the width of the photoresist pattern near the center of the base plate smaller than that near the peripheral portion, with the result that a predetermined desired photoresist pattern cannot be formed on the base plate.
On the other hand, in the spray method, the developer is sprayed from a spray nozzle having a predetermined spread angle so as to form a developer mist spreading, for example, in a conical form. Therefore, the spray method does not have the disadvantage of requiring a large amount of developer and a considerable amount of time for developing. However, the spray method has a disadvantage in that the thickness of the photoresist pattern formed on the base plate is uneven. Namely, bank-like ridges are formed on the peripheral portion of the resist film and result in irregularity of developing.